spin

Definition: Symbol s. The part of the total angular momentum of a particle, atom, nucleus, etc. that is distinct from its orbital angular momentum. A molecule, atom or nucleus in a specified energy level, or a particular elementary particle, has a particular spin, just as it has a particular charge or mass. According to quantum theory, this is quantised and is restricted to multiples of h/2π, where h is Planck's constant. Spin is characterised by a quantum number s. For example, for an electron, s=+/-½, implying a spin of +h/4π when it is spinning in one direction and -h/4 when it is spinning in the other. Because of their spin, particles also have their own intrinsic magnetic moments and in a magnetic field the spin of the particles lines up at an angle to the direction of the field, precessing around this direction.

Also Known As: spin angular momentum